We previously reported that
gelsolin gene expression is reduced in various
tumors. In an effort to gain further insights into the mechanism of
gelsolin downregulation in
tumors, we examined the in vivo properties of the
gelsolin promoter in
urinary bladder cancer cell lines. Neither mutation nor hypermethylation was responsible for gene silencing at the promoter. After exposure to
trichostatin A (
TSA), a
histone deacetylase inhibitor,
gelsolin promoter activity was markedly enhanced in the
cancer cells, not in cells derived from normal tissue.
Chromatin immunoprecipitation assays revealed that both
histones H3 and H4 were hypoacetylated in the promoter region of the
cancer cells, and the accumulation of acetylated
histones was detected by
TSA treatment. In vivo footprinting analysis revealed the presence of
dimethylsulfate (DMS) hypersensitive site in the
untranslated region around nucleotide--35 only in the
cancer cells but not in cells derived from normal tissue, and analysis of KMnO4 reactive
nucleotides showed that the stem loop structure could be formed in vivo of the
cancer cells. This novel stem loop structure may play a part in regulating the transcription of the
gelsolin gene in the
cancer cells. These results suggest that
nucleosome accessibility through
histone deacetylation and structural changes (DMS
hypersensitivity and stem loop structure) in the promoter region form the basis of the mechanism leading to the silencing of
gelsolin gene in human
bladder cancer.